Disclosed is an improvement in systems for the accurate registration of images on an image bearing member of an image reproduction system, such as a xerographic printer, especially a plural color printer, relative to other such images and/or other related components of the image reproduction system. In particular, there is disclosed in the embodiment herein an improved sensor and system for the detection of registration marks on the image bearing member. For example, the detecting of chevron shaped color toner image position registration marks on a photoreceptor belt with improvements in the shape and position of the active (light sensing) areas of the sensor.
The registration system disclosed in the specific embodiment herein can be accomplished with little or no additional cost or complexity over existing such registration systems. It can be accomplished with a relatively simple modification of pre-existing registration mark-on-belt (MOB) sensors and their controls, yet provide increased fine registration accuracy.
By way of background, in various reproduction systems, including xerographic printing, the control and registration of the position of imageable surfaces such as photoreceptor belts, intermediate transfer belts (if utilized), and/or images thereon, is critical, and a well developed art, as shown by the exemplary patents cited below. It is well known to provide various single and/or dual axes control systems, for adjusting or correcting the lateral position and/or process position or timing of a photoreceptor belt or other image bearing member of a reproduction apparatus, such as by belt lateral steering systems and/or belt drive motor controls, and/or adjusting or correcting the lateral position and/or process position or timing of the placing of images on the belt with adjustable image generators such as laser beam scanners.
An important application of such accurate image position or registration systems is to accurately control the positions of different colors being printed on the same intermediate or final image substrate, to insure the positional accuracy (adjacency and/or overlapping) of the various colors being printed. That is not limited to xerographic printing systems. For example, precise registration control may be required over different ink jet printing heads and/or vacuum belt or other sheet transports in a plural color ink jet printer.
Of particular interest here, it is well known to provide image registration systems for the correct and accurate alignment, relative to one another, on both axes, of different plural color images on an initial imaging bearing surface member such as (but not limited to) a photoreceptor belt of a xerographic color printer. That is, to improve the registration accuracy of such plural color images relative to one another and/or to the image bearing member, so that the different color images may be correctly and precisely positioned relative to one another and/or superposed and combined for a composite or full color image, to provide for customer-acceptable color printing on a final image substrate such as a sheet of paper. The individual primary color images to be combined for a mixed or full color image are often referred to as the color separations.
As noted, known means to adjust the registration of the images on either or both axes (the lateral axis and/or the process direction axis) relative to the image bearing surface and one another include adjusting the position or timing of the images being formed on the image bearing surface. That may be done by control of ROS (raster output scanner) laser beams or other known latent or visible image forming systems.
In particular, it is known to provide such imaging registration systems by means of marks-on-belt (MOB) systems, in which edge areas of the image bearing belt laterally outside of its normal imaging area are marked with registration positional marks, detectable by an optical sensor. For belt steering and motion registration systems (previously described) such registration marks can be permanent, such as by silk screen printing or otherwise permanent marks on the belt, such as belt apertures, which may be readily optically detectable. However, for image position control relative to other images on the belt, or the belt position, especially for color printing, typically these registration marks are not permanent marks. Typically they are distinctive marks imaged with, and adjacent to, the respective image, and developed with the same toner or other developer material as is being used to develop the associated image, in positions corresponding to, but outside of, the image position. Such as putting the marks along the side of the image position or in the inter-image zone between the images for two consecutive prints. Such marks-on-belt (MOB) image position or registration indicia are thus typically repeatedly developed and erased in each rotation of the photoreceptor belt. It is normally undesirable, of course, for such registration marks to appear on the final prints (on the final image substrate).
The above and further background, including examples of specific MOB registration sensors and controls, is well known to those skilled in this art, and taught in numerous products and patents thereon (of which the following are some examples). Thus, it need not be repeated herein in detail.
Of particular interest here, the following five Xerox Corp. U.S. patents are noted as specifically mentioning one or more registration systems utilizing xe2x80x9cchevronxe2x80x9d photoreceptor registration marks for color printing: U.S. Pat. Nos. 6,014,154; 5,774,156; 5,537,190; 5,418,556; and (of particular interest) U.S. Pat. No. 5,287,162, entitled xe2x80x9cMethod and Apparatus for Corrections of Color Registration Errors,xe2x80x9d issued Feb. 15, 1994 by deJong, et al., describing registration with chevrons and also bi-cell detectors or CCD detectors. The latter and other patents noted above, and other Xerox Corp. patents such as U.S. Pat. Nos. 5,748,221; 5,510,877 and 5,631,686, issued May 20, 1997 to Castelli, et al, are also relevant to MOB sensors and/or systems for image shifting into registration by ROS shifting and/or belt position shifting. Said U.S. Pat. No. 5,748,221, issued Nov. 1, 1995 to Castelli, et al, also describes chevron MOBs and bi-cells sensors.
Another MOB registration system for multicolor image registration which is disclosed as specific to intermediate image bearing belts (in addition to U.S. Pat. No. 5,287,162 above) is Fuji Xerox Co. U.S. Pat. No. 6,094,551. Also, U.S. Pat. No. 4,963,899 issued Oct. 16, 1990 to Resch, also describing bi-cell sensors.
U.S. Pat. No. 5,909,235 is of interest for noting MOB sensor registration, citation of other references here therein, and a background discussion of different applicable color printing systems, and U.S. Pat. No. 4,804,979 on MOBs.
The following exemplary U.S. patents are noted for discussions of photoreceptor or intermediate belt motion sensing with permanent belt fiducial or registration (and/or belt seam location) markings, by belt holes or other apertures, and optical sensors and/or belt steering controls: U.S. Pat. Nos. 4,837,636; 5,175,570; 5,204,620; 5,208,633; 5,248,027; 5,278,587 (on plural ROS beam sweep detections for single pass registered color printing) U.S. Pat. No. 5,383,014; and pending Xerox Corp. Ser. No. 09/450,375, filed Nov. 29, 1999 by Castelli, et al.
Of additional interest for registration of plural color images with sensed color registration marks on a belt is Xerox Corp. U.S. Pat. No. 5,384,592, issued Jan. 24, 1995 to Lam F. Wong, entitled xe2x80x9cMethod and Apparatus for Tandem Color Registration Control.xe2x80x9d
The following copending Xerox Corp. U.S. patent applications on color printer registration systems are also noted: Ser. No. 09/306,418, filed May 6, 1999, entitled xe2x80x9cOn-line Image-On-Image Color Registration Control Systems and Methods Based on Time-Scheduled Control Loop Switchingxe2x80x9d by Michael R. Furst, on a MOB sensor and control system; and Ser. No. 09/447,231, filed Nov. 23, 1999, entitled xe2x80x9cImage Color Registration Sensor Calibrationxe2x80x9d by Olga Ramirez and Mark Omelchenko, on MOB sensor calibration algorithms, disclosing chevron MOBs; and Ser. No. 09/626,465, filed Jul. 26, 2000, entitled xe2x80x9cColor Image Registration Based Upon Belt And Raster Output Scanner Synchronizationxe2x80x9d by Elias Panides, et al, on registering the leading edges of color images on a photoreceptor belt by ROS synchronization to belt registration holes.
As will be apparent from the above, it is generally well known in the art of reproduction systems that image registration control on an image bearing belt can be done based on MOB sensor measurements of developed marks on the belt indicative of respective image positions on that image bearing member (substrate). If desired, that can also be combined with additional sensor information from belt edge sensing and/or permanent belt marks or holes sensing. As also noted, a printer image registration controller and/or electronic front end (EFE) can utilize MOB sensor inputs to control ROS scan lines positioning on the photoreceptor (PR) surface to correct registration of the respective image positions on both axes. That is, without necessarily requiring MOB sensor interaction with, or control over, the PR drive or PR steering controls for process direction or lateral direction registration. However, such PR registration movement, instead of, or in addition to, such imaging position registration movement, can also be done if desired.
Further by way of background, the direct sensing of the surface motion of image receivers, such as photoreceptor belts or intermediate transfer belts, or other substrates, as by the system of the embodiment disclosed herein, enables more precise transport and/or image registration, for superior image quality.
By directly measuring the belt surface position with a high degree of accuracy, the sensor signals can be inputted into an agile beam imager, such as the variable imaging position ROS systems shown in FIGS. 1 and 2, to implement a printing system that can allow relaxation of motion control requirements or tolerances for the belt surface, and even potentially eliminating the need for an expensive precision belt movement rotary encoder and its circuitry.
Color registration systems for printing, as here, should not be confused with various color correction or calibration systems, involving various color space systems, conversions, or values, such as color intensity, density, hue, saturation, luminance, chrominance, or the like, as to which respective colors may be controlled or adjusted. Color registration systems, such as that disclosed herein, relate to positional information and positional correction (shifting respective color images laterally or in the process direction and/or providing image rotation and/or image magnification) so that different colors may be accurately superposed or interposed for customer-acceptable full color or intermixed color or accurately adjacent color printed images. The human eye is particularly sensitive to small printed color misregistrations of one color relative to one another in superposed or closely adjacent images, which can cause highly visible color printing defects such as color bleeds, non-trappings (white spaces between colors), halos, ghost images, etc.
In the exemplary embodiment herein there are disclosed known examples of developing xe2x80x9cchevronxe2x80x9d shaped registration marks on the photoreceptor (PR) beft, and sensing their positions, as taught in the above-cited and other patents and applications. Those features do not require detailed explanations herein other than for the specific improvements thereto disclosed herein. The disclosed system can otherwise desirably utilize essentially the same, existing, MOB sensor features of bi-cell photodiode chevron MOB detectors as taught in the above-cited and other patents, with low cost modifications as described herein. Therefor, only these modifications need be described and shown herein. Likewise, applications of the disclosed embodiments can utilize known or existing positional correction software and controls for ROS or other imaging position (and/or PR position) registration correction.
A specific feature of the specific embodiment disclosed herein is to provide in a plural color reproduction apparatus with a color registration system for the registration of plural color images on an image bearing surface movable in a process direction, which color registration system generates on said image bearing surface chevron shaped registration marks with opposingly angled legs at an angle to said process direction, and which color registration system further includes at least one registration marks sensor for detecting the positions of said chevron shaped registration marks on said image bearing surface, said registration marks sensor having chevron shaped optical sensing areas with opposingly angled legs at substantially the same opposing angles as said chevron shaped registration marks on said image bearing surface, the improvement wherein, said chevron shaped optical sensing areas of said registration marks sensor comprise a matching pair of spaced apart elongated bi-cell detectors in a generally chevron shaped pattern, each of said spaced apart elongated bi-cell detectors has a parallelogram shaped optical sensing area, and said parallelogram shape of each said bi-cell detector optical sensing area is defined by elongated parallelogram sides extending at the same angle as one said leg of said chevron shaped registration marks on said image bearing surface, and parallelogram ends which are parallel to said process direction, so as to provide higher color registration accuracy.
Further features disclosed in the embodiment herein, individually or in combination, include those wherein said image bearing surface is a photoreceptor of a xerographic printing system, and/or wherein said parallelogram shaped bi-cell detector optical sensing area is defined by two separate but directly adjacent parallelogram shaped photosensor areas of equal size.
The disclosed system may be operated and controlled by appropriate operation of otherwise conventional control systems in accordance with the descriptions herein. In particular is well known and preferable to program and execute control functions and logic for reproduction systems with software instructions for conventional microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, the disclosed control systems or methods may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
The term xe2x80x9creproduction apparatusxe2x80x9d or xe2x80x9cprinterxe2x80x9d as alternatively used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise indicated or defined in a claim. The term xe2x80x9csheetxe2x80x9d herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d or called a xe2x80x9chardcopyxe2x80x9d. A xe2x80x9cprint jobxe2x80x9d is normally a set of related sheets, usually one or more collated copy sets copied from a set of original document sheets or electronic document page images, from a particular user, or otherwise related.
As to specific components of the subject apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.